The present invention relates to refrigeration systems. More specifically, the present invention relates to refrigeration systems for refrigerated display cases for displaying products in a commercial application.
A retail store, such as a supermarket, typically contains many refrigerated display cases for displaying and cooling food and/or beverage items for sale. Many types of refrigerated display cases are known in the art, and are in extensive use in retail locations. Such refrigerated display cases require a refrigeration system to maintain a temperature within the display case that is lower than ambient temperature inside the store.
Refrigeration cycles are well-known in the art and generally include an evaporator, a compressor, and a condenser. A refrigerant fluid flows from one component to the next, exchanging heat so as to absorb heat from a refrigerated area and reject heat at the condenser, typically experiencing a phase change during the cycle.
A first prior art refrigeration system 20 is shown in FIG. 1. The refrigeration system 20 includes refrigeration units 24 that are each dedicated to a respective refrigerated display case 28. The refrigeration unit 24 for each refrigerated display case 28 includes a compressor (not shown) and a water-cooled condenser (not shown). The water-cooled condenser is cooled by a coolant fluid, typically a water/glycol mixture that is provided by a closed coolant loop 32 with associated coolant pumps 36. All the refrigerant for the refrigeration system is contained within the components of the refrigeration units 24, and a respective evaporator (not shown) in each refrigerated display case 28. Refrigerant fluid is heated and expanded in the evaporator as it removes heat from the refrigerated display case 28. The compressor compresses the heated refrigerant and forces it to flow to the water-cooled condenser in the refrigeration unit 24. The water-cooled condenser transfers heat from the refrigerant fluid to the coolant fluid, allowing the refrigerant fluid to condense, pass through an expansion valve, and return to the evaporator to be heated and expanded in a cyclical manner. The coolant pumps 36 in the closed coolant loop 32 force the cooling water/glycol mixture to flow to the water-cooled condenser from a heat exchanger 40 (e.g., an air-cooled fluid cooler), which is typically remotely located. At the heat exchanger 40, the coolant fluid is cooled and then returned to the water-cooled condenser to receive heat from the refrigerant fluid.
A second prior art refrigeration system 44 is shown in FIG. 2. Each refrigerated display case 52 includes an evaporator 56 for removing heat from each refrigerated display case 52. Evaporated refrigerant is routed from the evaporators 56 via a suction header 58 to a local bank of compressors 60 and then through a discharge header 62 to a remotely located condenser 64 to be condensed. Condensed refrigerant is routed from the condenser 64 via a liquid header 57 to the evaporators 56. The local bank of compressors 60 is located either at the end of a group or directly atop a group of refrigerated display cases 52 and contains several compressors connected in parallel within a sound-attenuated casing 66. The suction header 58 and the discharge header 62 are partially located within the sound-attenuated casing 66. The discharge header 62 establishes fluid communication between the local bank of compressors 60 and the condenser 64 and is not necessarily positioned adjacent each refrigerated display case 52. Similarly, the liquid header 57 establishes fluid communication between the evaporators 56 and the condenser 64, and is not necessarily positioned adjacent each refrigerated display case 52. The local bank of compressors 60 serves to compress heated refrigerant from several evaporators 56. The remotely located condenser 64 receives heated refrigerant from a single local bank of compressors 60.
A third prior art refrigeration system (not shown) is disclosed in U.S. Pat. No. 4,748,820. The third prior art refrigeration system includes a bank of centralized compressors located in an “equipment room” of a building, remotely located from a group of refrigerated display cases. The bank of centralized compressors supply compressed heated refrigerant gas via a discharge line to a condenser typically positioned outside of the building. From the condenser, cooled liquid refrigerant is routed via a liquid refrigerant line to evaporators positioned within the refrigerated display cases to cool a portion of each case. The evaporated refrigerant gas is then routed to a local booster compressor and then back to the bank of centralized compressors in the equipment room via individual suction lines from each refrigerated display case to repeat the cycle. The individual suction lines converge prior to the bank of centralized compressors in an interstage manifold located in the equipment room.
Upon startup or after a power outage of typical refrigeration systems, one or two small compressor units discharge refrigerant into a relatively long discharge header. Often, refrigerant in the room-temperature discharge header will condense and fill the discharge header with liquid refrigerant. In refrigeration systems that include a finite amount of refrigerant, the reduced availability of liquid refrigerant in the liquid header may be inadequate to properly cool the display cases. The reduced availability of refrigerant in the liquid header causes low suction in the system and may result in compressor shutoff due to very low suction pressures.